Airborne antenna coupled to adjustable helical counterpoise



R. ELLIS.

Aug. 4, 1970 Filed July 25, 1968 lll'lulllllllllll 250% was 3228 2525 25:2; 5 3528 m 358%. E as 5:5 m m mi x c 5552 m F 5:58 55 20:25:: 0 3253E8 E ww SE28 555 J ATTORNEY United States Patent,

US. Cl. 343-703 7 Claims ABSTRACT OF THE DISCLOSURE In place of theusual half-wave-length trailing antenna in very low frequency radiooperation from airborne vehicles, it is proposed to use a shorter, A1wave-length antenna and an adjustable tuning helix. Time required forplaying out and rewinding the antenna is reduced, antenna weight anddrag are lessened, and the weight of take-up machinery is decreased.Electrical insulation requirements are also lessened by the use of atuned helix for the counterpoise.

PRIOR ART The art of radio communication to and from an aeroplane is avery old one. Rouzet, in US. Pat. No. 1,106,729, shows a radiocommunication device in an aeroplane and shows a trailing or floatingwire antenna A. When the radio is operative, this wire antenna isunwound and then must be rewound by the winch C when the plane is aboutto land or when transmission has been completed.

This unwinding and rewinding is a consequence of the inherentcharacteristic of radio transmission and its velocity in any givenmedium is fixed. In the air, this velocity is about 300,000,000 meters/second. If high or very high frequencies of signaling are used, thewave-length (e.g. velocity/frequency) is short, and short antennae, suchas a so-called whip antenna, will sufiice. Such short antennae can bestructural parts of aeroplanes without serious aerodynamic drag orinsulation problems.

However, when low frequency transmission is necessary, for instance10,000 cycles per second, the wavelength becomes 30,000 (nearly 18miles). Even a quarterwave antenna, e.g. 4.5 miles of copper wire,represents an enormous weight. This weight, combined with theaerodynamic drag, creates a force which requires a material having ahigher tensile strength than copper alone to withstand the force. Astronger copper-clad Wire, such as a copper-steel alloy wire, has beensuggested for use but this further increases the weight to be carried bythe plane and further increases the size of the winding and unwindingmachinery needed.

Since the trailing antenna must be taken in before the plane may land,the take-up winch, such as C in Rouzet, must be quite powerful to effectthe rapid windup of several miles of steel-copper wire in an emergency.

The winch carrying the antenna wire is necessarily at the high potentialprevailing during radio transmission. In the very limited space in theaeroplane, a high potential mechanism, as large as an antenna winch,represents a constant electrical hazard to the crew members of theplane.

Fox US. Pat. No. 2,417,191 shows a trailing antenna on an aeroplane witha reel 3 to adjust the length of the antenna. As in Rouzet above, thereel 3 would be at high potential because the antenna counterpoise 16 isa fixed ground connection to the frame of the plane.

BRIEF DESCRIPTION The present invention eliminates the electrical hazardat the antenna winch. An airborne antenna is coupled to an adjustablehelical counterpoise so that the plane end of the antenna (a windingreel or winch) will be at ice or near zero potential. A ground to theplanes frame is not needed and details of the helix are given.

THE DRAWING FIG. 1 is the complete radio transmission and antennareeling system control, the container being shown in sections.

FIG. 1a is the electrical resonator system underlying the ungroundedtransmission of FIG. 1.

GENERAL DESCRIPTION In FIG. 1, a reel or winch R carries the antennawire A. The motor to drive the reel R and the motor control circuits arenot shown but may be any of the well-known systems for such powerdrives. A weight W has been found useful in avoiding whipping of theantenna against the body of the plane when the unreeled part is short.

Connected to the shaft of reel R is a revolution counter C. Counter C,in turn, is connected to indicator I which shows an observer how manyfeet of antenna are unreeled. Indicator I, preferably, is locatedadjacent the control unit SWITCH AND TAP CONTROL so that the observercan adjust both controls in accordance with the antenna length. Apreviously prepared CALIBRA- TION CHART assists the observer in settingthe controls.

The transmitter TX is coupled through an impedance balance monitor RX toa coupling circuit G which includes the primary winding of a transformerT. The secondary winding of the transformer T is divided into aplurality of sections. The two end sections are always in circuitbetween the antenna A and the counterpoise composed of a helix H. Theother secondary sections (four in the illustration) can beshort-circuited by tap switches TS. As illustrated, the second sectionfrom the right (antenna) end is not shorted and, thus, is in series withtwo end sections, the antenna and the counterpoise helix H.

From the above description, it will be seen that there is no groundconnection to the body of the plane and that, if the impedance of theantenna and the counterpoise helix H are kept equal, the reel end R ofthe antenna will not be at a high potential. Theoretically, the reelpotential can be practically zero.

The helix H comprises a frame D of dielectric material upon which arewound two spiral helical coils MVH and MH. The high voltage helix MVHconsists of several turns of relatively large conductor having an opencircuit termination TERM. The terminals TERM of this winding are spacedsuificiently far apart to avoid any arcing or corona discharges.

The main lateral winding MH has many turns and a plurality of taps MHTI,MHT, etc. connected thereto. Switches controlled by a switch controlenable most of the sections of the main helical winding MH to beshortcircuited. As shown in FIG. 1, 10 of the weight end of the coil areshort-circuited and 9 of the other end are not shorted.

As shown, the whole helix comprising MVH, MH, switches S, the switchcontrol and the dielectric framework D are contained in a conductive canor shield, this being shown in section in FIG. 1. Thus, inductionfeedback to the planes radio system and other electronic gear isprevented or reduced and the high voltage hazards for the crew arereduced.

Sharpness of tuning is best obtainable when the resistances in thetuning circuits are as low as possible. For this reason, the mainsection of the tuner MH is wound of the low resistance stranded silveror copper wire known as Litzendraht.

The operation of the helix H contactors, MHT MHT and the transformer Ttap switches T51, T52, TS3, etc. is effected from the switch and tapcontrol unit B. Electric-mechanical switches are preferred. Relay typeunits readily provide insulation between the low-voltage relay operatingcircuits and the high-voltages in the controls being switched. Purelymechanical switch operations can be used, if desired.

OPERATION When transmission is to be started with a selected wavelength, the reeling mechanism is run until the indicator I shows thecorrect length of antenna, then control unit B is set for the wavelength. When the transmitter TX is energized, the monitor RX indicatesany impedance mismatch 'between the counterpoise helix H and the antennaA. Changes in the control B or in the fine tuning adjustable condenserin coupler G can restore impedance match.

When a change in wave length is to be made while the transmitter is onthe reel, counter indicator I gives the attendant the information that,with the help of the previously prepared calibration chart, enables himto follow With an appropriate change in the setting of taps TS and MH.As before, a fine control of impedance match can be effected by theadjustable condenser in coupling circuit G.

FIG. 1a is an electrical simplification of the complete system inFIG. 1. The transmitter TX energizes a variable resonator in thecounterpoise helix and a second resonator in the trailing variablelength antenna.

Variations are possible in one or more of the elements of the presentdisclosure. I desire that it be understood that such modifications maybe made as are compatible with the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. In an air-borne radio system having a reeling device for a trailingantenna, an antenna counterpoise on board the aircraft, a trasformercoupling connected between said reeling device and said antennacounterpoise, a radio transmitter inductively coupled to saidtransformer coupling, the radio system being unconnected to the body ofthe aircraft, that improvement comprising:

(a) an indicator for said reeling device showing the length of antennatrailing from the aircraft;

(b) said antenna counterpoise on board the aircraft comprising a helicalwinding having adjustable taps thereon;

(c) said transformer coupling being provided with a plurality ofadjustable taps; and,

(d) control means for adjusting the taps in said antenna counterpoiseand said transformer coupling to a length compatible with that of thetrailing antenna as indicated by said indicator.

2. A system as claimed in claim 1, wherein said antenna counterpoisehelical winding is mounted on a dielectric framework and the winding andplurality of contacts are contained in a conductive housing.

3. A system as claimed in claim 2, wherein said dielectric frameworkalso carries a second open-circuited helical Winding conductively joinedto the first winding.

4. A system as claimed in claim 3, wherein said helical winding of saidantenna counterpoise is a fine stranded conductor and said secondhelical coil is wound of substantially larger Wire than that of saidantenna counterpoise.

5. A system as claimed in claim 1, wherein a previous ly preparedcalibration chart of antenna lengths and tap positions for taps on saidantenna counterpoise and said transformer coupling indicates theadjustments in said control means.

6. A system as claimed in claim 1, wherein said radio transmittercoupling includes a variable capacitor for fine tuning the coupling.

7. A system as claimed in claim 1 including an impedance monitor in saidradio transmitter coupling circuit.

References Cited UNITED STATES PATENTS 2,430,173 11/1947 Holmes 343707ELI LIEBERMAN, Primary Examiner US. Cl. X.R. 343707, 861

